In a related art, as an input device through which a user inputs desired information, a keyboard including a plurality of keys is used. The keyboard is excellent in convenience for the user to input desired information, but it is desirable that the keyboard has a certain size in order to include a plurality of keys each having the size that allows the user to operate the key. For example, a keyboard having so-called QWERTY key arrangement includes at least 26 keys that correspond to respective alphabetical letters.
In addition, a user interface by which a human operation is recognized, and desired information is input has been studied. For example, an input system discussed in Japanese Laid-open Patent Publication No. 2003-346162 recognizes which finger is extended by recognizing the shape of a hand from an input image, and input of an instruction or the like is performed based on the recognition result.